Method of making metal casting mold, and mold

ABSTRACT

A method of making a metal casting mold is disclosed. The method comprises the steps of: covering a support pattern by a pulp-molded element; installing a mold flask provided with a depressurizing device, on an upper side of the pulp-molded element; packing heat-resistant particles inside the mold flask; providing a sealing member on an upper surface of the mold flask so as to seal the inside of the mold flask; depressurizing the inside of the mold flask by the depressurizing device, to form a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member; and separating the pulp-molded element from the support pattern. A metal casting mold made by this method is also disclosed.

TECHNICAL FIELD

The present invention relates to a method of making a metal casting mold, and a metal casting mold.

BACKGROUND ART

Heretofore, there has been known a V-process casting method which comprises: tightly attaching a synthetic resin film onto a shaping surface of a master pattern member; packing dry sand on an outer side of the synthetic resin film; placing the dry sand under negative pressure to suck the synthetic resin film toward the dry sand; removing the master pattern member to form a cavity; and poring molten metal into the cavity, as described in the following Patent Document 1. In the V-process casting method, a mold is maintained by depressurizing an inside of the mold, i.e., a binder for binding molding sand is not used, so that a molding-sand mulling equipment becomes unnecessary. This also provides an advantage that odor during casting is seldom generated, and extraction of a product after casting is facilitated.

Patent Document 1: JP 50-8409 B

SUMMARY OF THE INVENTION Technical Problem

However, in the V-process casting method in the above Patent Document 1, it is necessary to apply a coating agent in order to prevent sticking of burned molding sand to molten metal, and to dry the applied coating agent.

The present invention has been made to solve the above problem, and an object thereof is to provide a metal casting mold making method and a mold which make it possible to produce a sound cast metal product free of sticking of burned molding sand to a surface thereof, without any need for the coating agent applying operation and the coating agent drying operation.

Solution to the Technical Problem

In order to achieve the above object, according to a first aspect of the present invention, there is provided a method of making a metal casting mold. The method comprises the steps of: covering a support pattern by a pulp-molded element; installing a mold flask provided with a depressurizing device, on an upper side of the pulp-molded element; packing heat-resistant particles inside the mold flask; providing a sealing member on an upper surface of the mold flask so as to seal the inside of the mold flask; depressurizing the inside of the mold flask by the depressurizing device, to form a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member; and separating the pulp-molded element from the support pattern.

In the first aspect of the present invention, the support pattern is covered by the pulp-molded element, so that the pulp-molded element is carbonized by heat of molten metal during casting to function as a coating agent, which makes it possible to prevent sticking of burned molding sand to a surface of a cast metal product. As a result, in the first aspect of the present invention, a need for applying the coating agent is eliminated, so that a coating agent applying operation and a coating agent drying operation, and any accompanying equipment, become unnecessary.

In the first aspect of the present invention, after sealing the upper surface of the mold flask by the sealing member, the inside of the mold flask filled with the heat-resistant particles is depressurized, so that the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member constituting the mold are integrated together, thereby providing enhanced strength of the mold, which makes it possible to make a mold using a pulp-molded element composed of natural fibers. In the first aspect of the present invention, the pulp-molded element is used, instead of using a synthetic resin film, so that it becomes possible to suppress gas generation due to burning of a synthetic resin film, and prevent surface defect of a cast metal product which would otherwise be caused by the gas generation.

In addition, differently from a synthetic resin film, the pulp-molded element does not use petroleum as its raw material, so that it becomes possible to contribute to reduce environmental burdens.

According to a second aspect of the present invention, there is provided a metal casting mold which comprises: a pulp-molded element covering a support pattern; a mold flask provided with a depressurizing device and installed on an upper side of the pulp-molded element; heat-resistant particles packed inside the mold flask; and a sealing member provided on an upper surface of the mold flask so as to seal the inside of the mold flask, wherein the depressurizing device is operable to depressurize the inside of the mold flask, thereby forming a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member, and allowing the pulp-molded element to be separated from the support pattern.

The second aspect of the present invention brings out the same excellent functions and effects as those in the first aspect of the present invention.

Preferably, in the second aspect of the present invention, the pulp-molded element is made of a natural fiber.

Preferably, in the second aspect of the present invention, the pulp-molded element has a thickness of 0.1 mm to 2.0 mm.

Preferably, in the second aspect of the present invention, the pulp-molded element is formed by a paper-making screen process.

Preferably, in the second aspect of the present invention, the pulp-molded element is formed by a paper pressing process.

According to a third aspect of the present invention, there is provided a method of making a metal casting mold. The method comprises the steps of: forming a pulp-molded element by using a paper-making pattern mold having a screen provided on a surface thereof; installing a mold flask provided with a depressurizing device, on an upper side of the pulp-molded element; packing heat-resistant particles inside the mold flask; providing a sealing member on a back surface of the mold flask so as to seal the inside of the mold flask; depressurizing the inside of the mold flask by the depressurizing device, to form a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member; and separating the pulp-molded element from the paper-making pattern mold.

According to a fourth aspect of the present invention, there is provided a method of making a metal casting mold. The method comprises the steps of: forming a pulp-molded element by using a paper-making pattern mold having a screen provided on a surface thereof; transferring the pulp-molded element to a support pattern; installing a mold flask provided with a depressurizing device, on an upper side of the pulp-molded element; packing heat-resistant particles inside the mold flask; providing a sealing member on a back surface of the mold flask so as to seal the inside of the mold flask; depressurizing the inside of the mold flask by the depressurizing device, to form a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member; and separating the pulp-molded element from the support pattern.

According to a fifth aspect of the present invention, there is provided a method of making a metal casting mold. The method comprises the steps of: forming a pulp-molded element having a core shape with at least one opening, by a combinational paper-making pattern mold having a molding surface divided into a plurality of regions and covered by a screen; inserting a depressurizing device from the opening into the pulp-molded element, and packing heat-resistant particles inside the pulp-molded element; sealing the opening of the pulp-molded element so as to prevent discharge of the heat-resistant particles packed inside the pulp-molded element; depressurizing the inside of the pulp-molded element by the depressurizing device, to form a core-shaped mold comprising the heat-resistant particles and the pulp-molded element; and separating the core mold having the pulp-molded element as a surface thereof, from the combinational paper-making pattern mold.

Preferably, the method according to the third or fourth aspect of the present invention further comprises, after the step of packing heat-resistant particles inside the mold flask, one selected from the group consisting of: a step of sucking air toward the side of a back surface of the paper-making pattern mold or the support pattern; a step of injecting pressurized air from the side of the back surface of the mold flask; and a step of injecting pressurized air from the side of the back surface of the mold flask, while sucking air toward the side of the back surface of the paper-making pattern mold or the support pattern.

Preferably, the method according to the fifth aspect of the present invention further comprises, after the step of packing heat-resistant particles inside the pulp-molded element, one selected from the group consisting of: a step of sucking air toward the side of a back surface of the combinational paper-making pattern mold; a step of injecting pressurized air from the opening of the pulp-molded element; and a step of injecting pressurized air from the opening of the pulp-molded element, while sucking air toward the side of the back surface of the combinational paper-making pattern mold.

Preferably, the method according to either one of the third to fifth aspects of the present invention further comprises a step of heating the heat-resistant particles.

Preferably, in the third to fifth aspects of the present invention, a heating temperature of the heat-resistant particles in the step of heating the heat-resistant particles is in the range of 50° C. to 200° C.

Preferably, in the third to fifth aspects of the present invention, the pulp-molded element has a thickness of 0.1 mm to 2.0 mm.

Preferably, in the third to fifth aspects of the present invention, the step of packing heat-resistant particles inside the mold flask or the pulp-molded element having a core shape includes a sub-step of packing heat-resistant particles under vibration.

According to a sixth aspect of the present invention, there is provided a metal casting mold made by the method according to either one of the third to fifth aspects of the present invention, wherein a product molding surface to be in contact with molten metal is a three-dimensional surface composed of the pulp-molded element, and a side behind the pulp-molded element is backed up by the heat-resistant particles and kept in a depressurized state.

Effect of the Invention

The metal casting mold making method and the mold of the present invention make it possible to produce a sound cast metal product free of sticking of burned molding sand to a surface thereof, without any need for the coating agent applying operation and the coating agent drying operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process diagram illustrating a metal casting mold making method according to a first embodiment of the present invention.

FIG. 2 is a sectional view illustrating a structure of a mold assembly in a mold-closing-state before pouring of molten metal, in the method according the first embodiment of the present invention.

FIG. 3 is a process diagram illustrating a metal casting mold making method according to a second embodiment of the present invention.

FIG. 4 is a process diagram illustrating an example of modification of each metal casting mold making method according to the second embodiment and the following third embodiment of the present invention.

FIG. 5 is a process diagram illustrating a metal casting mold making method according to a third embodiment of the present invention.

FIG. 6 is a process diagram illustrating a metal casting mold making method according to a fourth embodiment of the present invention.

FIG. 7 is a process diagram illustrating an example of modification of the metal casting mold making method according to the fourth embodiment of the present invention.

FIG. 8 is a top plan view illustrating a mold assembly made by the metal casting mold making methods according to the second to fourth embodiments of the present invention.

FIG. 9 is a sectional view taken along the line A-A in FIG. 8.

FIG. 10 is a sectional view taken along the line B-B in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to accompanying drawings, a metal casting mold making method and a mold of the present invention will now be described.

First of all, based on FIGS. 1 and 2, a metal casting mold making method and a mold according to a first embodiment of the present invention will be described.

As illustrated in FIG. 1(A), a support pattern 1, a pulp-molded element (shielding member) 2 and a mold flask 4 are preliminarily prepared, and then a concavoconvex surface of the support pattern 1 is covered by the pulp-molded element 2.

In this embodiment, the support pattern 1 is a mount configured to have an upper surface with concavities and convexities conforming to a shape of a cavity, and bearingly support the pulp-molded element 2 while placing the pulp-molded element 2 to cover the concavoconvex surface. The mold flask 4 is a frame member in which an upper surface (back surface) 4 a and a lower surface 4 b are opened. The mold flask 4 is provided with a depressurizing mechanism 6 for depressurizing an inside of the mold flask 4.

The pulp-molded element 2 is a member which shields an opening on the side of a mold-mating surface (lower surface 4 b) of the mold flask 4. The pulp-molded element 2 is formed in a region which forms the mold-mating surface and a surface of the cavity, and covers at least the concavoconvex surface of the support pattern 1. As used here, the term “cavity (14)” means a space defined in an inside of a mold assembly 12 obtained by mating an upper mold 12 a and a lower mold 12 b together, wherein molten metal is poured into this space to thereby produce a cast metal product (see FIG. 2).

Then, as illustrated in FIG. 1(B), the mold flask 4 is installed on an upper side of the pulp-molded element 2. Subsequently, as illustrated in FIG. 1(C), heat-resistant particles 8 are packed inside the mold flask 4, i.e., into a space defined by the pulp-molded element 2 and the mold flask 4. During the operation of packing the heat-resistant particles 8 inside the mold flask 4, it is preferable to vibrate the mold flask 4 to improve a packing density of the heat-resistant particles 8 in the inside of the mold flask 4. After completion of the packing of the heat-resistant particles 8, a sealing member 10 is provided on the upper surface of the mold flask 4, so that the inside of the mold flask 4 is sealed by the sealing member 10.

Subsequently, the inside of the mold flask 4 is depressurized by the depressurizing mechanism 6. When the inside of the mold flask 4 is depressurized, the pulp-molded element 2 is sucked toward the heat-resistant particles 8, and thereby a mold is formed in which the mold flask 4, the heat-resistant particles 8, the pulp-molded element 2 and the sealing member 10 are integrated together.

In this embodiment, the depressurizing mechanism 6 comprises: a plurality of pipes 6 a each composed of a net with fine meshes precluding passage of the heat-resistant particles 8 as described later and disposed in the inside of the mold flask 4; and a suction chamber 6 b and a suction port 6 c which are formed inside the mold flask 4 and with which opposite ends of each of the plurality of pipes 6 a communicate. The suction port 6 c is connected to a suction device (not illustrated) provided externally, to allow the inside of the mold flask 4 to be sucked (depressurized) via the pipes 6 a.

Subsequently, as illustrated in FIG. 1(D), in a state in which the depressurization of the inside of the mold flask 4 is maintained, the pulp-molded element 2 is separated from the support pattern 1. The inside of the mold flask 4 will be continuously depressurized by the depressurizing mechanism 6.

FIG. 2 illustrates a mold assembly 12 obtained by mating together an upper mold 12 a and a lower mold 12 b each made by the process illustrated in FIG. 1.

In this embodiment, the pulp-molded element 2 is preliminarily molded by a paper-making screen process or a paper pressing process. As used here, the teem “paper-making screen process” means a process of: collecting a raw material dissolved in water and formed as slurry, by a screen (metal mesh) bonded onto a pattern mold; and drying the collected slurry to obtain a pulp-molded element having a desired shape. On the other hand, the “paper pressing process” is a process for obtaining a pulp-molded element having a desired shape by pressing a planar-shaped paper. The paper-making screen process has an advantage of being able to obtain a pulp-molded element having a complicated shape. On the other hand, the paper pressing process has an advantage of being able to reduce a production cost, although an obtainable shape is limited to a simple shape.

As a raw material for the pulp-molded element 2, it is possible to use wood pulp typified by paper pulp, and other natural fiber pulps, such as cotton pulp, cotton linter pulp, bamboo pulp, straw pulp and other non-wood pulps. These raw materials for the pulp-molded element may be virgin pulp, or may be recycled/used paper pulp or mixed pulp of them. The recycled-paper pulp is preferable in view of environment and production cost. It is also possible to use non-natural fibers, such as synthetic resin fibers, although it cannot be said that they are desirable in view of environment and production cost.

The pulp-molded element 2 is formed to have a thickness of 0.1 mm to 2.0 mm. If the thickness is set to be less than 0.1 mm, a strength of the pulp-molded element 2 is deteriorated, which causes a problem that tearing, wrinkle, etc., occurs during installation onto the support pattern 1. On the other hand, if the thickness is greater than 2.0 mm, an unreasonable situation occurs, for example, in which a size of a resulting cast mold product is excessively increased by a value corresponding to a reduction in thickness of the pulp-molded element due to its carbonization, volume reduction and thinning caused by heat of molten metal during casting, although there is no major problem in production of cast metal.

As a material for the pulp-molded element 2, a type having an average pulp fiber length of 0.3 mm to 4.0 mm is used. If the length is less than 0.3 mm, the strength of the pulp-molded element is deteriorated. On the other hand, if the length is greater than 4.0 mm, unevenness in thickness of a resulting paper is more likely to occur.

Preferably, the pulp-molded element 2 for use in a mold in this embodiment has an average pulp fiber length of about 2 mm, and a thickness of 1 mm, in view of handleability, gas permeability, releasability of a cast metal product from sand, etc.

As described above, in the metal casting mold making method and the mold according to the first embodiment of the present invention, the pulp-molded element is used as a cavity surface, so that the pulp-molded element is carbonized by heat of molten metal during casting to function as a coating agent, which makes it possible to prevent sticking of burned molding sand to a surface of a cast metal product. As a result, a need for applying the coating agent is eliminated, so that a coating agent applying operation and a coating agent drying operation, and any accompanying equipment, become unnecessary.

In the first embodiment, after sealing openings of the lower and upper surfaces of the mold flask by the pulp-molded element (shielding member) and the sealing member, the inside of the mold flask filled with the heat-resistant particles is depressurized, so that a strength of a mold is increased, which makes it possible to make a mold using a pulp-molded element composed of natural fibers. In the first embodiment, differently from the V-process casting method, no synthetic resin film is used as a shielding member, so that it becomes possible to suppress gas generation due to burning of a synthetic resin film, and prevent surface defect of a cast metal product which would otherwise be caused by the gas generation. In addition, differently from a synthetic resin film, the pulp-molded element using natural fibers in the first embodiment does not use petroleum as its raw material, so that it becomes possible to contribute to reduce environmental burdens.

In the first embodiment, binder-free particles, such as binder-free sand, are used as the heat-resistant particles to be packed inside the mold flask, so that odor or harmful gas is not generated, which eliminates a need for any accompanying equipment, such as an exhaust-gas treatment device. In addition, the heat-resistant particles, such as sand, have no need for adding binder thereto, so that it is not necessary to perform a treatment using a mulling machine, etc., which provides large advantageous effects, such as reduction in the number of processes, reduction of apparatuses, and reduction of management operations. In the first embodiment, when the mold is disassembled, the molding sand can be broken down by releasing the depressurization of the inside of the mold flask to set a pressure therein to normal pressure, so that the breaking down does not require vibration, hammering or the like, and dust diffusion is minor, which makes it possible to scale down accompanying equipment, such as a dust collector.

Next, based on FIG. 3, a metal casting mold making method and a mold according to a second embodiment of the present invention will be described.

First of all, as illustrated in FIG. 3(A), in order to obtain a desired cast metal product, a three-dimensionally-shaped pulp-molded element 22 is formed by a paper-making screen process using a paper-making pattern mold 20 provided with a screen (metal mesh) on a surface thereof Then, as illustrated in FIG. 3(B), a mold flask 28 having opened upper and lower surfaces and comprising a depressurizing mechanism 26 capable of depressurizing an inside thereof is provided on an upper surface of the pulp-molded element 22 in such a manner as to allow aftermentioned heat-resistant particles 24 to be packed therein. The depressurizing mechanism 26 is the same type as the depressurizing mechanism 6 in the first embodiment.

Subsequently, after providing a molten metal pouring sprue, a flow-off for molten metal, etc., according to need, heat-resistant particles 24 are packed into a space surrounded by the pulp-molded element 22 and the mold flask 28, as illustrated in FIG. 3(C). Then, as illustrated in FIG. 3(D), a back surface (upper surface) of the mold flask 28 is sealed against atmospheric air by a sealing member 30, such as a synthetic resin film, so as to allow an inside of the mold flask 28 to be depressurized. Subsequently, the inside of the mold flask 28 is depressurized through the depressurizing mechanism 26 to form a mold in which the mold flask 28, the heat-resistant particles 24, the pulp-molded element 22 and the sealing member 30 are integrated together. Then, as illustrated in FIG. 3(E), in a state in which the depressurization of the inside of the mold flask 28 is maintained to continually suck the pulp-molded element 22 toward the mold flask 28, the pulp-molded element 22 is released from the paper-making pattern mold 20.

During the mold release, air may be injected from the side of a back surface (lower surface) of the paper-making pattern mold 20 to facilitate the release. Although a synthetic resin film is used as the sealing member in this embodiment, the sealing member is not limited thereto, but any other suitable material, such as an iron plate or a rubber sheet, may be used. Further, as the heat-resistant particles 24, casting sand, such as silica sand, may be used.

In the second embodiment, when the pulp-molded element 22 absorbs moisture during the above process, it can become difficult to achieve a desirable situation during casting. Thus, it is necessary to dry the pulp-molded element 22. For this purpose, it is preferable that, after forming the pulp-molded element 22, the heat-resistant particles 24 to be packed are heated up to a temperature of 50° C. to 200° C., and the pulp-molded element 22 is dried by heat of the heat-resistant particles 24. In this case, as compared to a conventional drying method, a drying time for the pulp-molded element 22 is shortened, and problems, such as deformation and residual water due to uneven heating, are solved. The heating temperature of the heat-resistant particles 24 is set in the range of 50° C. to 200° C., because, if the temperature is less than 50° C., an effect of drying the pulp-molded element 22 is insufficient, whereas, if the temperature is greater than 200° C., water in the pulp-molded element 22 is instantaneously vaporized immediately after a contact between the heat-resistant particles 24 and the pulp-molded element 22, which is likely to cause scattering of the heat-resistant particles 24.

In the second embodiment, after the step of packing the heat-resistant particles 24 inside the mold flask 28, a step of sucking air toward the side of the back surface (lower surface) of the paper-making pattern mold 20, or a step of injecting pressurized air from the back surface (upper surface) of the mold flask 28, or a step of injecting pressurized air from the side of the back surface (upper surface) of the mold flask 28, while sucking air toward the side of the back surface (lower surface) of the paper-making pattern mold 20, as illustrated in FIG. 4, may be performed. In the embodiment illustrated in FIG. 4, a pressurized air supply box 32 is provided on the back surface (upper surface) of the mold flask 28, to inject pressurized air, while sucking air toward the side of the back surface (lower surface) of the paper-making pattern mold 20. When airflow is formed in this way, drying of the pulp-molded element 22 can be further accelerated.

Next, based on FIG. 5, a metal casting mold making method according to a third embodiment of the present invention will be described.

In the third embodiment, after forming a pulp-molded element 22 by a paper-making pattern mold 20, as illustrated in FIG. 5(A), a support pattern 34 is put over the paper-making pattern mold 20. The support pattern 34 has a structure obtained by inverting a configuration of the paper-making pattern mold 20, i.e., has a surface profile capable of coming into close contact with the pulp-molded element 22.

Then, after transferring the pulp-molded element 22 from the paper-making pattern mold 20 to the support pattern 34, as illustrated in FIG. 5(B), a mold flask 28 is provided on the pulp-molded element 22 on an upper surface of the support pattern 34, whereafter, in the same manner as that in the second embodiment illustrated in FIG. 3, a mold is fabricated by; packing heat-resistant particles 24 (see FIG. 5(D)); sealing a back surface (upper surface) of the mold flask 28 by a sealing member 30 (see FIG. 5(E)); depressurizing an inside of the mold flask 28 to form a mold in which the mold flask 28, the heat-resistant particles 24, the pulp-molded element 22 and the sealing member 30 are integrated together; and releasing the pulp-molded element 22 from the paper-making pattern mold 20 while maintaining the depressurization (see FIG. 5(F)). During the pattern release, air may be injected from the side of a lower surface of the support pattern 34 to facilitate the release.

In the third embodiment, it is preferable that a heating temperature of the heat-resistant particles 24 is set in the range of 50° C. to 200° C., and the pulp-molded element 22 is dried by heat of the heat-resistant particles 24, as with the second embodiment. Further, as illustrated in FIG. 4, after the step of packing the heat-resistant particles 24 inside the mold flask 28, a step of sucking air toward the side of a back surface (lower surface) of the support pattern 34, or a step of injecting pressurized air from the side of the back surface (upper surface) of the mold flask 28, or a step of injecting pressurized air from the side of the back surface (upper surface) of the mold flask 28, while sucking air toward the side of the back surface (lower surface) of the support pattern 34, as illustrated in FIG. 4, may be performed.

Next, based on FIG. 6, a metal casting mold making method according to a fourth embodiment of the present invention will be described. The fourth embodiment relates to a process for making a metal casting core mold.

First of all, as illustrated in FIG. 6(A), a bag-like pulp-molded element 42 is formed by a combinational paper-making pattern mold 40 which has a molding surface divided into two or more regions and covered by a screen (metal mesh), and defines therein a core shape having at least one core print region opened to the outside.

Then, as illustrated in FIG. 6(B), a depressurizing mechanism 44 for depressurizing an inside of the bag-like pulp-molded element 42 is inserted from the opening, and heat-resistant particles 46 are packed. Subsequently, as illustrated in FIG. 6(C), a part of the heat-resistant particles 46 adjacent to the opening are impregnated with a binder 48 such as wax, and bound to seal the opening so as to prevent discharge of the heat-resistant particles 46 packed inside the bag-like pulp-molded element 42. Subsequently, the inside of the bag-like pulp-molded element 42 is depressurized through the depressurizing mechanism 44 to form a mold in which the heat-resistant particles 46 and the pulp-molded element 42 are integrated together. Then, as illustrated in FIG. 6(D), in a state in which the depressurization of the inside of the bag-like pulp-molded element 42 is maintained, the core mold 50 having the bag-like pulp-molded element 42 as a surface thereof is released from the combinational paper-making pattern mold 40.

During the mold release, as illustrated in FIG. 6(D), air may be injected (blown off) from the side of a back surface (outer surface) of the paper-making pattern mold 40 to facilitate the release. As an alternative method for sealing the opening so as to prevent discharge of the heat-resistant particles packed inside the pulp-molded element, the opening may be closed by using a sealing member capable of sealing atmospheric air, such as a synthetic resin film.

In the fourth embodiment, in view of drying of the bag-like pulp-molded element 42, it is preferable that a heating temperature of the heat-resistant particles 46 to be packed is set in the range of 50° C. to 200° C. Further, after the step of packing the heat-resistant particles 46, a step of sucking air toward the side of the back surface of the combinational paper-making pattern mold 40, or a step of injecting pressurized air from the opening of the bag-like pulp-molded element 42, or a step of injecting pressurized air from the opening of the bag-like pulp-molded element 42, while sucking air toward the side of the back surface of the combinational paper-making pattern mold 40, as illustrated in FIG. 7, may be performed. As an alternative method for injecting pressurized air, pressurized air may be injected from a connection section 44 c with to a suction device (not illustrated), by using the depressurizing mechanism 44. Alternatively, for example, pressurized air may be injected using a pressurized air supply box (see FIG. 4) covering the opening of the pulp-molded element 42, or may be injected from a nozzle or the like directly into the opening of the pulp-molded element 42.

In the second to fourth embodiments, dry thicknesses of the pulp-molded elements 22, 42 are preferably in the range of 0.1 to 2.0 mm. If the thickness is less than 0.1 mm, a stable pulp-molded element cannot be obtained, specifically, a partial tearing is more likely to occur. On the other hand, if the thickness is greater than 2.0 mm, an unreasonable situation occurs, for example, in which a size of a resulting cast mold product is excessively increased by a value corresponding to a reduction in thickness of the pulp-molded element due to its carbonization, volume reduction and thinning caused by heat of molten metal during casting, although there is no major problem in production of cast metal.

In the second to fourth embodiments, a suitable average pulp fiber length of the pulp-molded element is in the range of 0.3 mm to 4.0 mm. If the length is less than 0.3 mm, the strength of the pulp-molded element is deteriorated. On the other hand, if the length is greater than 4.0 mm, unevenness in thickness of a resulting paper is more likely to occur. Preferably, the pulp-molded element has a fiber length of about 0.8 to 3.5 mm, and a thickness of 0.5 to 1.5 mm, in view of handleability during paper making, gas permeability, releasability of a cast metal product from sand, etc.

In the second to fourth embodiments, with a view to enhancing the packing density of the heat-resistant particles (24, 46), it is preferable to pack the particles while applying vibration to the mold flask. Although no serious packing defect occurs in artificial casting sand having an almost uniform spherical shape, the packing with vibration is extremely effective, particularly, in casting sand having non-uniform shapes, such as silica sand. In addition to casting sand, it is possible to use, as the heat-resistant particles (24, 46), commonly-used sand or gravel, glass beads, ceramic beads, or metal particles.

Next, based on FIGS. 8 to 10, a metal molding mold assembly made by the second to fourth embodiments will be described. FIG. 8 is a top plan view illustrating the mold assembly made by the metal casting mold making methods according to the second to fourth embodiments of the present invention, and FIG. 9 and FIG. 10 are, respectively, a sectional view taken along the line A-A in FIG. 8, and a sectional view taken along the line B-B in FIG. 8.

As illustrated in FIGS. 8 to 10, the metal molding mold assembly comprises a main mold 52 as a mold assembly made by any one of the second to third embodiments, and a core mold 50 as a mold made by the fourth embodiment. In each of the molds 50, 52, a product molding surface to be in contact with molten metal is a three-dimensional surface defined by the pulp-molded element (22, 42), and a side behind the pulp-molded element (22, 42) is backed up by the heat-resistant particles (24, 46) and kept in a depressurized state.

In such a metal molding mold assembly (50, 52), a surface to be in contact with high-temperature molten metal is composed of the pulp-molded element (22, 42). Although the pulp-molded element (22, 42) is carbonized during casting, generation of harmful gas and odor can be mostly suppressed by employing natural fiber. Further, the heat-resistant particles (24, 46) are binder-free, so that odor or harmful gas is not generated, which eliminates a need for any accompanying equipment, such as an exhaust-gas treatment device. In addition, the heat-resistant particles (24, 46) have no need for adding binder thereto, so that it is not necessary to perform a treatment using a mulling machine, etc., which provides large advantageous effects, such as reduction in the number of processes, reduction of apparatuses, and reduction of management operations.

When the mold is disassembled, the casting sand can be broken down by releasing the depressurization of an inside of each mold to set a pressure therein to normal pressure. Although it is observed that a carbonized layer of the pulp-molded element loosely adheres onto a cast metal product, the cast metal product can be readily separated from the heat-resistant particles. Further, the breaking down does not require vibration, hammering or the like, and dust diffusion is low, which provides an advantage that there is almost no need to take into account accompanying equipment, such as a dust collector.

EXAMPLES

Examples 1 to 5 of the first embodiment of the present invention will be described below.

Example 1

As a molding material for a pulp-molded element, an aqueous solution of bleached kraft paper recycled-paper pulp (average fiber length: 3.5 mm) having a solid content concentration of about 1 weight % was preliminarily prepared by experimentally defiberizing bleached kraft paper in the form of a pulp slurry.

As a paper-making pattern mold, a paper-making aluminum pattern mold having a 100-mesh screen bonded onto a surface thereof was preliminarily prepared.

In order to form a pulp-molded element, the paper-making aluminum pattern mold was immersed in the pulp slurry while stirring the pulp slurry, and vacuum suction of the pulp slurry was done so that the pulp was sucked and layered on the paper-making aluminum pattern mold, whereafter the paper-making aluminum pattern was extracted from the pulp slurry.

Then, in order to dehydrate the pulp-molded element, one of a pair of compressing mating dies was put over the paper-making aluminum pattern mold having the pulp-molded element layered thereon to transfer the pulp-molded element to the compressing mating die, and then the other compressing mating die was mated therewith to dry the pulp-molded element while blowing off hot air. In this dried state, the pulp-molded element has a thickness of about 0.5 mm.

In regard to a configuration of the pulp-molded element, walls of a gating system for casting, such as a sprue, a runner and an ingate, were formed integrally together with a cavity surface for forming a product. However, the walls of the gating system are not necessarily formed integrally together therewith. In the case where the walls of the gating system are not formed integrally together with the pulp-molded element, before packing heat-resistant particles inside a mold flask, pattern elements made by paper pulp or foamed polystyrene may be connected to the pulp-molded element.

In the same manner, another pulp-molded element for the other mating mold of the mold assembly was formed.

Then, a mold making operation was performed. The pulp-molded element was put on a support pattern composed of a resin block so as not to form a gap therebetween. When there is a gap between the support pattern and the pulp-molded element, a certain level of dimensional adjustment can be performed by pressing the pulp-molded element against the support pattern while spraying water onto the pulp-molded element, to allow them to conform to each other. In this example, with a view to enhancing the packing density of heat-resistant particles packed inside a mold flask, the support pattern was placed on a vibration table.

Then, a mold flask equipped with a depressurizing mechanism capable of depressurizing an inside of the mold flask was put on the pulp-molded element, and heat-resistant particles are packed inside the mold flask while operating the vibration table. As the heat-resistant particles, artificial casting sand (NAIGAI CERABEADS 650 produced by Itochu Ceratech Corporation) was used.

Subsequently, after putting a synthetic resin film having a thickness of about 0.05 mm, over an upper surface of the mold flask to isolate the inside of the mold flask from atmospheric air, the inside of the mold flask was depressurized by a vacuum pump, and the pulp-molded element was released from the support pattern. The inside of the mold flask was depressurized to 250 to 300 mm Hg. If there is difficulty in releasing the pulp-molded element (shielding member) due to its air permeability, the support pattern may have a mechanism for blowing off air therefrom to facilitate the pattern release.

In the same manner, the other mating mold was made to complete the metal molding mold assembly.

Cast iron at about 1400° C. was cast into the mold assembly made in the above manner.

As a result, during casting, dust diffusion seldom occurred, and no odor was felt. After cooling, the depressurization of the mold was released, and a cast metal product was extracted. The mold could be disassembled without dust diffusion and odor. Further, only a thin carbonized layer loosely adhered on a surface of the cast metal product, and no adhesion on sand was observed. The cast metal product could be cast with sound quality without blow hole, pin hole, sand burning, etc.

Example 2

As a molding material for a pulp-molded element, an aqueous solution of milk carton recycled-paper pulp (average fiber length: 2 mm) having a solid content concentration of about 1 weight % was preliminarily prepared by experimentally defiberizing milk carton in the form of a pulp slurry and removing therefrom a film and others laminated thereon.

The pulp-molded element was formed in the same manner as that in Example 1. A thickness of the pulp-molded element was set to about 1 mm. In this example, the pulp-molded element is fabricated together with a gating system, such as a sprue, a runner and an ingate.

Then, a mold making operation and a casting operation were performed in the same manner as that in Example 1.

As a result, through the entire process, for example, during casting and during mold disassembly, dust diffusion and odor seldom occurred without causing pollution in working environment, etc. In addition, sound quality could be ensured in a resulting cast metal product.

Example 3

As a molding material for a pulp-molded element, an aqueous solution of newspaper recycled-paper pulp (average fiber length: 0.8 mm) having a solid content concentration of about 1 weight % was preliminarily prepared by experimentally defiberizing newspaper in the form of a pulp slurry and deinking the pulp slurry.

The pulp-molded element was formed in the same manner as that in Example 1. A thickness of the pulp-molded element was set to about 1.5 mm. In this example, the pulp-molded element is fabricated together with a gating system, such as a sprue, a runner and an ingate.

Then, a mold making operation and a casting operation were performed in the same manner as that in Example 1, except that silica sand (Australian Flattery sand) was used as the heat-resistant particles.

As a result, through the entire process, for example, during casting and during mold disassembly, generation of odor seldom occurred. However, as compared to the artificial casting sand in Example 1, dust diffusion was slightly observed but it was not at a level exerting an influence on working environment.

A resulting cast metal product was obtained with sound quality, as with Examples 1 and 2.

Example 4

As a molding material for a pulp-molded element, an aqueous solution of newspaper recycled-paper pulp (average fiber length: 0.4 mm) having a solid content concentration of about 1 weight % was preliminarily prepared by experimentally defiberizing newspaper in the form of a pulp slurry and deinking the pulp slurry.

The pulp-molded element was formed in the same manner as that in Example 1. A thickness of the pulp-molded element was set to about 2.5 mm. In this example, the pulp-molded element is fabricated together with a gating system, such as a sprue, a runner and an ingate.

Then, a mold making operation and a casting operation were performed in the same manner as that in Example 3. As a result, through the entire process, for example, during casting and during mold disassembly, generation of odor seldom occurred. However, as compared to the artificial casting sand in Example 1, dust diffusion was slightly observed but it was not at a level exerting an influence on working environment.

A resulting cast metal product was obtained with sound quality, as with Example 3. However, because the thickness of the pulp-molded element was 2.5 mm, the occurrence of burrs on a mold-mating surface was observed.

Example 5

In this example, a pulp-molded element was formed in the same manner as that in Example 4, except that an outer peripheral portion of the pulp-molded element around a product molding surface is pressed from the side of a back surface thereof in a range of about 3 mm width by using a separately prepared jig, to allow of the outer peripheral portion of the pulp-molded element to have a wall thickness of about 0.8 mm. In this example, the pulp-molded element is fabricated together with a gating system, such as a sprue, a runner and an ingate.

Then, a mold making operation and a casting operation were performed in the same manner as that in Example 4.

As a result, a resulting cast metal product was significantly improved in terms of burrs.

Next, Examples 6 to 9 of the second to fourth embodiments of the present invention will be described.

Example 6

In advance of fabrication of a pulp-molded element, an aqueous solution of bleached kraft paper recycled-paper pulp (average fiber length: 3.5 mm) having a solid content concentration of about 0.5 weight % was preliminarily prepared by experimentally defiberizing bleached kraft paper in the form of a pulp slurry. As a paper-making pattern mold, a paper-making aluminum pattern mold having a 100-mesh screen bonded onto a surface thereof was preliminarily prepared.

In order to form a pulp-molded element, the paper-making aluminum pattern mold was immersed in the pulp slurry while stirring the pulp slurry, and vacuum suction of the pulp slurry was done so that the pulp was sucked and layered on the paper-making aluminum pattern mold, whereafter the paper-making aluminum pattern mold was extracted from the pulp slurry.

Then, a mold flask capable of allowing an inside thereof to be depressurized was put on an upper side of the pulp-molded element, and artificial casting sand (NAIGAI CERABEADS 650 produced by Itochu Ceratech Corporation) serving as heat-resistant particles were heated up to about 60° C. and packed into a space surrounded by the pulp-molded element and the mold flask, while operating a vibration table to enhance a packing density of the artificial casting sand. Subsequently, air was sucked toward the side of a back surface of the paper-making pattern mold to generate airflow passing through the mold flask. A period of time of the airflow generation was about 60 seconds.

Subsequently, after putting a synthetic resin film having a thickness of about 0.05 mm, over a back surface of the mold flask to isolate the inside of the mold flask from atmospheric air, the inside of the mold flask was depressurized by a vacuum pump, and the pulp-molded element was released from the paper-making pattern mold. The pulp-molded element has air-permeability, and therefore it is necessary to take measures to facilitate the mold release. In this regard, the pulp-molded element could be easily released from the paper-making pattern mold by injecting air from the side of the back surface of the paper-making pattern mold during the mold release. In this state, a thickness of the pulp-molded element was about 0.5 mm.

In regard to a configuration of the pulp-molded element, walls of a sprue, a runner, an ingate and others required for casting were formed integrally together with a product molding surface (cavity surface). Then, a pair of mating molds each having the pulp-molded element as a molding surface were made in the same way, and mated together to make up a casting mold assembly. Cast iron at about 1400° C. was cast into the mold assembly.

As a result, during casting, dust diffusion seldom occurred, and no odor was felt. After cooling, the depressurization of the mold was released, and a cast metal product was extracted. The mold could be disassembled without dust diffusion and odor. Further, only a thin carbonized layer loosely adhered on a surface of the cast metal product, and no adhesion on sand was observed. The cast metal product could be cast with sound quality without blow hole, pin hole, sand burning, etc.

Example 7

In advance of fabrication of a pulp-molded element, an aqueous solution of milk carton recycled-paper pulp (average fiber length: 2 mm) having a solid content concentration of about 0.5 weight % was preliminarily prepared by experimentally defiberizing milk carton in the form of a pulp slurry and removing therefrom a film and others laminated thereon.

A mold was fabricated in the same manner as that in Example 6. Specifically, the thickness of the pulp-molded element was set to about 1 mm, and the temperature of the heat-resistant particles was set to about 100° C. Further, the period of time of the in-mold airflow generation for drying the pulp-molded element was set to about 90 seconds. A casting operation was performed in the same manner as that in Example 6.

As a result, through the entire process, for example, during casting and during mold disassembly, dust diffusion and odor seldom occurred without causing pollution in working environment, etc. In addition, sound quality could be ensured in a resulting cast metal product.

Example 8

In advance of fabrication of a pulp-molded element, an aqueous solution of newspaper recycled-paper pulp (average fiber length: 0.8 mm) having a solid content concentration of about 0.5 weight % was preliminarily prepared by experimentally defiberizing newspaper in the form of a pulp slurry and deinking the pulp slurry. A mold was fabricated in the same manner as that in Example 6, except that silica sand (Australian Flattery sand) was used as the heat-resistant particles, and packed inside the mold flask while applying vibration thereto. The thickness of the pulp-molded element was set to about 1.5 mm, and the temperature of the heat-resistant particles was set to about 150° C. Further, the period of time of the in-mold airflow generation for drying the pulp-molded element was set to about 60 seconds.

As a result, through the entire process, for example, during casting and during mold disassembly, generation of dust and odor seldom occurred. However, as compared to the artificial casting sand in Example 6, dust diffusion was slightly observed. A resulting cast metal product was obtained with sound quality, as with Examples 6 and 7.

Example 9

In advance of fabrication of a pulp-molded element, an aqueous solution of milk carton recycled-paper pulp (average fiber length: 2 mm) having a solid content concentration of about 0.5 weight % was preliminarily prepared by experimentally defiberizing milk carton in the form of a pulp slurry and removing therefrom a film and others laminated thereon.

In advance of fabrication of a core mold, a core shape illustrated in FIG. 6 was formed by a two-divided paper-making pattern mold. A 100-mesh screen was put over a paper-making surface. A core print region of the core mold was opened to the outside to allow the pulp-molded element forming slurry to get in and out through this opening. In an operation of forming the pulp-molded element, the two-divided paper-making pattern mold was set in a closing state, and immersed in the slurry bath. The slurry was entered from the opening of the core print region, and sucked toward the side of a back surface of the paper-making pattern mold to thereby form a pulp-molded element.

Then, the paper-making pattern mold was extracted from the slurry bath, and heat-resistant particles heated up to 100° C. were packed from the opening into the mold. Concurrently, a pipe-shaped depressurizing mechanism was inserted so as to depressurize an inside of the mold. Subsequently, pressurized air was injected from the opening into the mold, while sucking air toward the side of the back surface of the paper-making pattern mold, to dry the pulp-molded element. A period of time of the pressurization and suction was set to about 60 seconds.

Then, a core mold was fabricated by: putting a synthetic resin film having a thickness of about 0.05 mm, over the opening to shield the opening to allow the inside of the mold to be depressurized; depressurizing the inside of the mold through the depressurizing mechanism; and simultaneously injecting air between the pulp-molded element and the paper-making pattern mold to separate them from each other. A thickness of the pulp-molded element was set to about 1 mm.

Separately from the above operations, upper and lower main cores fabricated in the same manner as that in Example 7 were preliminarily prepared. Then, the above core mold was installed in the lower mold, and the upper mold was put thereon to make up a casting mold assembly as illustrated in FIG. 8. A casting operation was performed in the same manner as that in Example 6.

As a result, through the entire process, for example, during casting and during mold disassembly, generation of dust and odor seldom occurred without causing pollution in working environment, etc. In addition, sound quality could be ensured in a resulting cast metal product.

EXPLANATION OF REFERENCE NUMERALS

1, 34: support pattern

2, 22, 42: pulp-molded element

4, 28: mold flask

6, 26, 44: depressurizing mechanism (depressurizing device)

8, 24, 46: heat-resistant particles

10, 30: sealing member

20, 40: paper-making pattern mold 

1. A method of making a metal casting mold, comprising the steps of: covering a support pattern by a pulp-molded element; installing a mold flask provided with a depressurizing device, on an upper side of the pulp-molded element; packing heat-resistant particles inside the mold flask; providing a sealing member on an upper surface of the mold flask so as to seal the inside of the mold flask; depressurizing the inside of the mold flask by the depressurizing device, to form a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member; and separating the pulp-molded element from the support pattern.
 2. A metal casting mold comprising: a pulp-molded element covering a support pattern; a mold flask provided with a depressurizing device and installed on an upper side of the pulp-molded element; heat-resistant particles packed inside the mold flask; and a sealing member provided on an upper surface of the mold flask so as to seal the inside of the mold flask, wherein the depressurizing device is operable to depressurize the inside of the mold flask, thereby forming a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member, and allowing the pulp-molded element to be separated from the support pattern.
 3. The metal casting mold according to claim 2, wherein the pulp-molded element is made of a natural fiber.
 4. The metal casting mold according to claim 2, wherein the pulp-molded element has a thickness of 0.1 mm to 2.0 mm.
 5. The metal casting mold according to claim 2, wherein the pulp-molded element is formed by a paper-making screen process.
 6. The metal casting mold according to claim 2, wherein the pulp-molded element is formed by a paper pressing process.
 7. A method of making a metal casting mold, comprising the steps of: forming a pulp-molded element by using a paper-making pattern mold having a screen provided on a surface thereof; installing a mold flask provided with a depressurizing device, on an upper side of the pulp-molded element; packing heat-resistant particles inside the mold flask; providing a sealing member on a back surface of the mold flask so as to seal the inside of the mold flask; depressurizing the inside of the mold flask by the depressurizing device, to form a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member; and separating the pulp-molded element from the paper-making pattern mold.
 8. A method of making a metal casting mold, comprising the steps of: forming a pulp-molded element by using a paper-making pattern mold having a screen provided on a surface thereof; transferring the pulp-molded element to a support pattern; installing a mold flask provided with a depressurizing device, on an upper side of the pulp-molded element; packing heat-resistant particles inside the mold flask; providing a sealing member on a back surface of the mold flask so as to seal the inside of the mold flask; depressurizing the inside of the mold flask by the depressurizing device, to form a mold comprising the mold flask, the heat-resistant particles, the pulp-molded element and the sealing member; and separating the pulp-molded element from the support pattern.
 9. A method of making a metal casting mold, comprising the steps of: forming a pulp-molded element having a core shape with at least one opening, by a combinational paper-making pattern mold having a molding surface divided into a plurality of regions and covered by a screen; inserting a depressurizing device from the opening into the pulp-molded element, and packing heat-resistant particles inside the pulp-molded element; sealing the opening of the pulp-molded element so as to prevent discharge of the heat-resistant particles packed inside the pulp-molded element; depressurizing the inside of the pulp-molded element by the depressurizing device, to form a core-shaped mold comprising the heat-resistant particles and the pulp-molded element; and separating the core mold having the pulp-molded element as a surface thereof, from the combinational paper-making pattern mold.
 10. The method according to claim 7, which further comprises, after the step of packing heat-resistant particles inside the mold flask, one selected from the group consisting of: a step of sucking air toward the side of a back surface of the paper-making pattern mold; a step of injecting pressurized air from the side of the back surface of the mold flask; and a step of injecting pressurized air from the side of the back surface of the mold flask, while sucking air toward the side of the back surface of the paper-making pattern mold.
 11. The method according to claim 8, which further comprises, after the step of packing heat-resistant particles inside the mold flask, one selected from the group consisting of: a step of sucking air toward the side of a back surface of the support pattern; a step of injecting pressurized air from the side of the back surface of the mold flask; and a step of injecting pressurized air from the side of the back surface of the mold flask, while sucking air toward the side of the back surface of the support pattern.
 12. The method according to claim 9, which further comprises, after the step of packing heat-resistant particles inside the pulp-molded element, one selected from the group consisting of: a step of sucking air toward the side of a back surface of the combinational paper-making pattern mold; a step of injecting pressurized air from the opening of the pulp-molded element; and a step of injecting pressurized air from the opening of the pulp-molded element, while sucking air toward the side of the back surface of the combinational paper-making pattern mold.
 13. The method according to claim 7, which further comprises a step of heating the heat-resistant particles.
 14. The method according to in claim 13, wherein a heating temperature of the heat-resistant particles in the step of heating the heat-resistant particles is in the range of 50° C. to 200° C.
 15. The method according to claim 7, wherein the pulp-molded element has a thickness of 0.1 mm to 2.0 mm.
 16. The method according to claim 7, wherein the step of packing heat-resistant particles inside the mold flask includes a sub-step of packing heat-resistant particles under vibration.
 17. The method according to claim 9, wherein the step of packing heat-resistant particles inside the pulp-molded element includes a sub-step of packing heat-resistant particles under vibration.
 18. A metal casting mold made by the method according to claim 7, wherein a product molding surface to be in contact with molten metal is a three-dimensional surface composed of the pulp-molded element, and a side behind the pulp-molded element is backed up by the heat-resistant particles and kept in a depressurized state. 